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DEAP-3600 Dark Matter Detector: Advancements and Collaborators

DEAP-3600, a detector targeting dark matter using liquid argon, boasts high coherence, PSD for background/g discrimination, and substantial target masses. This large-scale project involves a 85 cm radius acrylic sphere housing 3600 kg of liquid argon, with collaborators from multiple universities and research institutions. The shield tank prevents cryogen mixing, while the water shielding minimizes (a,n) from rock. Key US and Canadian groups are collaborating on this significant experiment.

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DEAP-3600 Dark Matter Detector: Advancements and Collaborators

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  1. DEAP-3600 and the Cryopit SNOLAB Cube Hall Feb 2010 Location of the DEAP-3600 shield tank. @ Mark Boulay Queen’s University, Kingston DEAP EAC Meeting August 16, 2011

  2. Liquid argon as a dark matter target • Less loss of coherence for lighter nuclei, • argon can provide useful information even • with relatively high energy threshold Rate ~ A2F (coherent) • Well-separated singlet and triplet lifetimes in argon allow for good • pulse-shape discrimination (PSD) of b/g’s using only scintillation time • information, projected to 10-10 at 20 keVee • (see Astroparticle Physics 25, 179 (2006) and arxiv/0904.2930) • Very large target masses possible, since no absorption of UV scintillation photons in argon, and no e-drift requirements. • 1000 kg argon target allows 10-46 cm2sensitivity (SI) with ~20 keVee threshold, 3-year run 40Ar c 40Ar c

  3. Plot courtesy of Wolfgang Rau XENON100 arXiv:1104.2549 80 keVr threshold, without depletion of 39Ar CDMS 2010: 612 kg-days (Ge) XENON100 2011: 1471 kg-days (Xe) DEAP-3600: 1,000,000 kg-days (LAr) background free sensitivity

  4. DEAP-3600 Detector 85 cm radius acrylic sphere contains 3600 kg LAr (55 cm, 1000 kg fiducial, sealed vacuum vessel to control backgrounds) 8” PMTs (warm PMTs to increase light efficiency) 50 cm acrylic light guides and fillers for neutron shielding (from PMTs) Steel shell for safety to prevent cryogen/water mixing (AV failure) Only LAr, acrylic, and WLS (10 g) inside of neutron shield 8.5 m diameter water shielding sized for reduction of (a,n) from rock

  5. DEAP collaborators (Canadian groups) • University of Alberta D. Grant, P. Gorel, A. Hallin, J. Soukup, C. Ng, B. Beltran, K. Olsen • Carleton University K. Graham, C. Ouellet • Queen's University M. Boulay, B. Cai, D. Bearse, K. Dering, M. Chen, S. Florian, R. Gagnon, V.V. Golovko, M. Kuzniak, J.J. Lidgard, A. McDonald, A.J. Noble, E. O’Dwyer, P. Pasuthip, T. Pollman, W. Rau, T. Sonley, P. Skensved, M. Ward • SNOLAB/Laurentian B. Cleveland, F. Duncan, R. Ford, C.J. Jillings, M. Batygov, E. Vazquez Jauregui • SNOLAB I. Lawson, K. McFarlane, P. Liimatainen, O. Li • TRIUMF F. Retiere, Alex Muir

  6. DEAP/CLEAN collaborators • University of Alberta: P. Gorel, A. Hallin, J. Soukup, C. Ng, B. Beltran, K. Olsen • Boston University:D. Gastler, E. Kearns • Carleton University: K. Graham, C. Ouellet • Harvard: J. Doyle • Los Alamos National Laboratory: C. Alexander, S.R. Elliott, V. Gehman, V. Guiseppe, W. Louis, A. Hime, K. Rielage, S. Siebert, J.M. Wouters • MIT:J. Monroe, J. Formaggio • University of New Mexico: F. Giuliani, M. Gold, D. Loomba • NIST Boulder: K. Coakley • University of North Carolina: R. Henning, M. Ronquest • University of Pennsylvania: J. Klein, A. Mastbaum, G. Orebi-Gann • Queen's University: M. Boulay, B. Cai, D. Bearse, K. Dering, M. Chen, S. Florian, R. Gagnon, V.V. Golovko, M. Kuzniak, J.J. Lidgard, A. McDonald, A.J. Noble, E. O’Dwyer, P. Pasuthip, T. Pollman, W. Rau, T. Sonley, P. Skensved, M. Ward • SNOLAB/Laurentian:B. Cleveland, F. Duncan, R. Ford, C.J. Jillings, M. Batygov • SNOLAB:I. Lawson, K. McFarlane, P. Liimatainen, O. Li • University of South Dakota:D.-M. Mei • Syracuse University: R. Schnee, M. Kos, B. Wang • TRIUMF: F. Retiere, A. Muir • Yale University: W. Lippincott, D.N. McKinsey, J. Nikkel CAD groups primarily focused on DEAP-3600 US groups: miniCLEAN (includes LNe target, solar neutrino R&D)

  7. DEAP-3600 Background Budget (3 year run) PSD Acr+H2O shield Resurfacer, reconstruction Need to resurface inner vessel and ensure purity of TPB and acrylic (40 mm layer, including surface)

  8. From DEAP-STR-2011-009 (BeiCai)

  9. Neck connects to vacuum and Gas/liquid lines UHVwindows poly PMT supports 11” x 6” (8” CF) tee 8” long acrylic guide Acrylic vacuum chamber ET 9390B PMT 5” inner surface 97% diffuse reflector, Covered with TPB wavelength shifter 7 kg LAr DEAP-1 prototype (7 kg LAr)

  10. R5912 HQE PMTs on DEAP-1 (Feb. 2010) KobyDering mineral oil optical coupling identical to DEAP-3600 design

  11. Light yield in DEAP-1 with Hamamatsu R5912 HQE PMTs >4 pe/keVin DEAP-1 expect higher light yield in DEAP-3600 (greater PMT coverage, 75% vs 20%) MC simulations (ratio of DEAP-3600 to DEAP-1) show > 6pe/keVin DEAP-3600, meets design spec.

  12. Calibration of DEAP-1 with AmBe neutron source

  13. β/γ backgrounds • 39Ar is the most dominant β/γ background • Expect 109 events in 3 years in (20-40) keVee • Pulse-shape discrimination in DEAP-1 extrapolates to sufficient PSD • Working with Princeton group for 4 tonnes depleted argon for DEAP-3600 (>50 times depletion)

  14. a Backgrounds in Liquid Argon Decay inbulk argon tagged by a-particle energy a Decay from TPB surface releases untagged recoiling nucleus in argon and ain TPB (see both with low energy) a Decay from TPB surface releases a in argon and recoil nucleus in TPB (see mostly a-particle, high energy) Decay from inside TPB or acrylic releases a which may also enter LAr. Could see (a) Light from TPB only (prompt) or (b) Light from LAr (range of energies) 210Po on surface both TPB and LAr scintillate TPB PTFE Acrylic LAr DEAP-1 and DEAP-3600 surface profile

  15. a Backgrounds in LAr (DEAP-1) 210Po 232Th chain June 2010 PTFE TPB 238U chain Acrylic LAr DEAP-1 data Events/100 keV In DEAP-1: 100 mBq222Rn 20 mBq220Rn 222Rn+220Rn

  16. Background rates in DEAP-1 (low-energy region 120-240 p.e.)

  17. Chris Jillings – CAP Congress 2011 – Memorial University Detector Chamber: Gen III Neutron-like events

  18. Chris Jillings – CAP Congress 2011 – Memorial University Radon Spike Used a spike of 222Rn captured from SNOLAB air Introduced into argon system Low-energy events in center of detector increased tens of minutes before high-energy events. The large peaks at high z-fit did not increase. Argon inlet

  19. Chris Jillings – CAP Congress 2011 – Memorial University Detector Chamber: Gen IV, V Better plug at neck Better endcaps

  20. Chris Jillings – CAP Congress 2011 – Memorial University Gen IV Backgrounds

  21. Surface backgrounds in DEAP-1/DEAP-3600 (Toy model of fitter response) Backgrounds in DEAP-1 dominated by surface events. Projected sensitivity of 2x10-46 cm2 with DEAP-1 background levels after position reconstruction. (Those are upper limit: near levels of Radon emanation, neutrons in DEAP-1)

  22. DEAP and miniCLEAN shield tanks at SNOLAB

  23. Current Status DEAP-3600 Full capital funding (~10 M$) announced summer 2009, cash flow Nov. 2010 Construction of infrastructure at SNOLAB (support deck and shielding tanks complete, water purification systems, chillers, etc. being installed) Construction of acrylic vessel at Reynolds Polymer about to begin; will be machined at U of A and installed in Cube Hall. U of A mill upgraded for vessel machining. 20” test vessel has been constructed and bonded at Reynolds Polymer

  24. Current Status DEAP-3600 • Several large components ordered/fabricated: • ultralow-background, highly transparent acrylic (> several m attenuation length) for light guides (Spartech) • August 10 production start • HQE PMTs (first 100 PMTs now in-house at Queen’s being characterized) • VME digitizing electronics (at TRIUMF) • Large LN2 dewar and 3 KW cryocooler system being fabricated (Stirling) • Slow controls system in-house at Queen’s • Argon purification system under development • “Resurfacer” device under development • Continued materials assay and qualification

  25. 20” Test Vessel Machining at Alberta

  26. 20” Test Vessel at the University of Alberta Vessel now fully bonded at Reynolds; will be shipped to Queen’s in September for cryogenic/QA testing.

  27. DEAP-3600 Acrylic Vessel Construction/Assembly Panels are thermoformed and bonded into a spherical shell and neck collar/neck (Reynolds Polymer in Colorado) Shell is machined (U of A) to include light guide “stubs” Light guides are bonded on (UG due to transport constraints) onto stubs: Vessel must be rotated to allow bonding of each light guide in approximately horizontal position Full vessel is annealed Not trivial to scale to significantly larger size!

  28. Acrylic light guide bonding at Alberta

  29. Light guide bonding at U of A • Developed well-controlled bonding system • Bond parameters are monitored to ensure • consistency • Many test bonds completed, standard LN2 • “shock” tests for QA

  30. Future Plans Plan to explore possibility of “scaling-up” single-phase liquid argon, by a factor of ~10 Currently no detailed design or timeline (focus is currently on DEAP-3600). Some considerations: Larger experiment would require depleted argon, and significant storage facility; need to evaluate dominant residual backgrounds in argon after 39Ar (including residuals from muons/spallation) Safety considerations for large cryogenic target need to be implicit in detector design (especially water shielding/flooding, ODH vent, seismic concerns, and any large dewars) Experiment much larger than DEAP-3600 should have simplified optical readout (and lower background to reduce requirement for neutron shielding), simplified acrylic vessel (still require “sealed” inner volume for radon reduction), but should be simple to install (perhaps non-structural flat panels?) Scintillation light readout should in principle be possible at larger scales.

  31. Possible timeline for Cryopit Current plan is to operate DEAP-3600 and collect some data/gain experience before making decision to seek funding for next scale experiment Earliest we would consider seeking funding (for detector engineering) is around 2013; still unclear whether larger detector would require Cryopit, but certainly a possibility Planning some modest feasibility studies in coming year (combination of simulations and evaluating possible designs)

  32. Summary DEAP-3600 detector under construction in SNOLAB cube hall, target sensitivity is 10-46 cm2 Single-phase liquid argon technology should be scalable to much larger target masses; no detailed technical design study yet completed for DEAP scale-up Plan to collect initial data with DEAP-3600 before deciding to pursue funding for larger experiment (2013 earliest date to seek funds) Experiment at this scale (likely ~50 M$) would require v. significant collaboration and several funding partners Larger detector could require Cryopit, significant work to define infrastructure and safety requirements

  33. END

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